The use of phase encoding for modulating a digital data signal is well known. Such phase encoding comprises varying the phase of a digital signal so as to represent one or more data bits with each phase transition.
For example, if four different phases, e.g., 0.degree., 90.degree., 180.degree., and 270.degree., are used, then causing the phase to recede, to be reduced from 0.degree. to 270.degree., reduced from 90.degree. to 0.degree., reduced from 180.degree. to 90.degree., or reduced from 270.degree. to 180.degree., may be utilized to represent a the binary number 0; and similarly, advancing the phase, i.e., from 0.degree. to 90.degree., 90.degree. to 180.degree., 180.degree. to 270.degree., 270.degree. to 0.degree., may be utilized to represent the binary number 1.
The use of such phase encoding has the potential to offer a degree of noise immunity while facilitating comparatively high data rates.
However, such phase encoding is susceptible to noise interference when very high data rates are utilized, especially when the level of the transmitted signal is very low, such as when spread spectrum techniques are utilized.
In view of the foregoing, it would be beneficial to provide means for decoding phase encoded digital data communications which provides for a high degree of reliability, particularly when high data rates are utilized with low power signals, such as those common in spread spectrum communications, particularly in electrically noisy environments.